Distillation, Azeotropic and Extractive

Abstract

Many industrial processes depend on efficient separation methods for azeotropic or other close‐boiling or low relative volatility mixtures. Whereas ordinary distillation is either uneconomical or impossible in these cases, the addition of specially chosen separating agents can generally facilitate the separation. Four of the five principal techniques employed are discussed: extractive or homogeneous azeotropic distillation, where the liquid separating agent is completely miscible; heterogeneous azeotropic distillation, where the agent, known as the entrainer, forms one or more azeotropes but causes immiscibility; distillation in the presence of ionic salts, which alters the relative volatilities of the components; and pressure‐swing distillation, where a series of columns operate at different pressures. Residue curve maps, material balance lines, and column sequences are given for several commercially important systems. Methods for evaluating total annualized costs are also discussed as are models for determining feasible separating agents.

Process Designs for Separating R-410A, R-404A, and R-407C Using Extractive Distillation and Ionic Liquid Entrainers

“…12 Extractive distillation separations include organic/water, olefin/paraffin (alkene/ alkane), aliphatic/aromatic hydrocarbons, and aromatic/ aromatic hydrocarbons. 13 Extractive distillation uses an additional solvent, an entrainer, to alter the liquid phase properties and modify the volatility of each component, resulting in a more efficient separation. The entrainer absorbs one of the components to carry the solute to the bottom of the column while the other component is distilled out the top of the column.…”

Advances in Extractive Distillation

“…4,8,12 Based on the possible RCM types, ED can be divided into three categories: separation of minimum-boiling or maximum-boiling azeotropes (see Figure 2, right) and the separation of low relative-volatility non-azeotropic mixtures. 4,8,12 Based on the possible RCM types, ED can be divided into three categories: separation of minimum-boiling or maximum-boiling azeotropes (see Figure 2, right) and the separation of low relative-volatility non-azeotropic mixtures.…”

Entrainer Selection and Systematic Design of Heterogeneous Azeotropic Distillation Flowsheets

“…7,8,35 These bounds are influenced by nonideal interactions in the liquid phase and by how these interactions impact the relative volatility in both magnitude and order. 34 Consequently, the feasibility constraints on extractive distillation are system specific and cannot be generalized in contrast to the former two split types.…”

“…Saddle − Saddle Split: S − S. Heterogeneous Extractive Distillation. Examining the RCM that represents mixtures separable using extractive distillation, the so-called “extractive map”, , we can define the extractive distillation task as the splitting of two nonadjacent saddle products in the same distillation region from an overall feed in the same region. With this definition in mind, we found that the concept of extractive distillation must be combined with the exploitation of liquid−liquid immiscibility to carry out the main task in some of the RCM classes studied in section 4, where cells of type II or type IV exist.…”